I develop an exact truthmaker semantics in the style of Kit Fine’s unilateral semantics, with special attention to the semantics of negation, which I base on a binary exclusion relation that represents a kind of incompatibility. My truthmakers are Davidsonian events, including negative events, which turn out to play a useful role in accounts of perception reports and other constructions. I discuss connections to possible world semantics and situation semantics. I argue for treating propositions as sets of events. I present evidence from counterfactuals with complex antecedents for this idea and for the cumulative nature of the exclusion relation. Parts of this project are joint work with Timothée Bernard (CNRS / Paris 7).